Partially devitrified glasses



Dec. 10, 1963 B. V. JANAKIRAMARAO PARTIALLY DERITRIFIED GLASSES FiledOct. 6, 1960 3 Sheets-Sheet 1 Fig.

Bhoguraju V. Janukiroma-Roo ZMQZ/Q/ ATTORNEY 10, 1963 B. v.JANAKlRAMA-RAO 3,113,377

PARTIALLY DERITRIFIED GLASSES Filed 001:. 6, 1960 3 Sheets-Sheet 2 Fig.3

INVENTOR. Bhogoraju V. dc nakirclma-Roo ATTORNEY 1963 B. v.JANAKlRAMA-RAO 7 PARTIALLY DERITRIFIED GLASSES Filed Oct. 6, 1960 5Sheets-Sheet 3 Heat Treatment Schedule Fig. 5

Temperatu re F MOULDING TE MP.

Time in Hours INVENTOR. Bhogaruju V. Jonakimmo-Rao ATTORNEY UnitedStates Patent Office 3,113,87'1 Patented Dec. 10, l9ti3 3,113,877RARTIALLY DEViTRlFlEl) GLASSES Bhogara u Janalrirama-ltao, Philadelphia,Pa., assignor to International Resistance Qompany, Philadelphia, Pa.Filed Oct. 6, 1960, Ser. No, 69,853 6 Claims. (Cl. 106--52) The presentinvention relates to ceramics, and more particularly to partiallydevitrified glasses.

Completely vitrified ceramics, i.e. glasses, have a great many uses.However, the physical properaties, such as mechanical strength andability to withstand heat, and the electrical properties, such asdielectric constant and dissipation factor, of glasses have limited theuse of lass. Although, the previously mentioned physical and eleclricalproperties of the semi-crystalline ceramics, such as porcelain,refractory bodies and the like, are better than that of glass, thesemi-crystalline ceramics have a disadvantage over glasses in the mannerthat they are made.

Glasses can be melted so that glass objects of various shapes can bemade relatively easily in properly shaped molds. Also, glass objects canbe made quickly so that many of such objects can be inexpensively massproduced. However, the method of making the semi-crystalline ceram cobjects is relatively slow and comprises many steps including forming,drying and firing. Therefore it would be desirable to have a ceramicwhich could be made 1n the same manner as glasses, but which would haveimproved physical and electrical properties.

It IS an object of the present invention to provide a novel ceramic.

It is another object of the present invention to provide a novel ceramichaving physical and electrical properties better than those of acorresponding glass, but which can be made in a manner similar to aglass.

It IS a further object of the present invention to provide a partiallydevitrified glass.

It is still a further object of the present invention to provide a glasshaving a controlled amount of devitriiication to improve the propertiesof the glass.

Other objects will appear hereinafter.

The invention accordingly comprises a composition of matter possessingthe characteristics, properties, and the relation of constituents whichwill be exemplified in the FOIIIPO-SXIIOH hereinafter described, and thescope of he invention will be indicated in the claims. y

For a fuller understanding of the nature and objects of the nvention,reference should be had to the followin detailed description taken inconnection with the accom panymg drawings in which:

FIGURE 1 is a triaxial diagram showing the ranges in percent by weightof the ingredients used to form the silica, potash, titanium oxide glasssystem of the present invention, with the shade area indicating rangesover which the partially devitrified glass of the present inventron isformed.

FIGURE 2 is a triaxial diagram similar to FIGURE 1 for a silica, potash,niobium oxide glass system of the present invention.

FIGURE 3 is a triaxial diagram similar to FIGURE 1 for a silica, potash,tantalum oxide glass system of the present invention.

FIGURE 4 is a triaxial diagram similar to FIGURE 1 for a germaniumoxide, potash, tantalum oxide glass system of the present invention.

FIGURE 5 is a graph illustrating various heat treatment schedules forobtaining the partially devitrified glasses of the present invention.

Heretofore, the phenomenon of devitrification or phase separation inglass has been considered undesirable, and therefore avoided, sincecomplete devitrification resulted in a solid formed mainly of a mass ofcrystals with little or no adhering bond. However, I have discoveredthat if devitrification is deliberately induced according to plan, andthe amount of devitrification controlled, the resultant article willhave improved properties, such as a higher deformation temperature,better reflectivity, opacity, and better electrical properties, such asdielectric constant, and dissipation factor. Although any glasscomposition theoretically, devitrifies if held long enough at itsdevitrification temperature, this manner of devitrification to obtain acontrolled amount of devitrification is commercially uneconomical sincethe heat treatment to achieve this mannor of devitrification couldextend to hundreds or thousands of hours. However, I have discoveredthat by introducing certain nucleating agents, such as titanium oxide(TiO tantalum oxide (Ta O and niobium oxide (Nb O into certain baseglass compositions, such as a silica-potash or a germanium oxide-potashcomposition, and by properly heating such glasses, it is possible tomake glasses with a controlled amount of devitrification and withimproved physical, chemical and electrical properties withincommerically feasible time limits.

In general, the glasses of the present invention are made by mixingtogether and placing in a refractory crucible or tank furnace the finelypowdered batch components in the form of oxides, carbonates, nitrates,or other compounds which will yield when melted the required. amount ofcation content, such batch components being of an amount sulhcient toprovide the proper percentage calculated on weight percent of oxidebasis. The crucible and its contents are then heated in a furnace to atemperature sufficient to melt the contents, and the contents of thecrucible are maintained at such temperature for a period sufficient toinsure complete melting of the batch components. The molten glass isthen formed into desired shapes using well known forming techniques,such as pressing, drawing, blowing, etc. The formed objects of the glassof the ent invention may then be annealed using well known annealingtechniques. Such annealing includes heating the glass object to theannealing temperature, and maintaining the object at the annealingtemperature for a period of time suilicient to permit relief of thestrains in the glass. The glass object is then cooled at a rate toprevent excessive strains from reforming in the glass. Up to this pointthe method of making the glasses of the present invention follows thewell known, conventional practice for making glasses. At this stage inthe making of the glass of the present invention, the glass iscompletely vitrified and is transparent.

To form the partially devitrified glass of the present invention, theglass object is heated to a temperature of from F. to 300 F. above theannealing temperature of the glass, and held at such temperature from 1to 4 hours to initiate nucleation. Such nucleation consists of myriadsof ultramicroscopic nuclei being formed in the glass by the nucleatingcations. The glass article is then heated to a temperature slightlyabove the deformation temperature of the object in its completelyvitrified, glassy state, and held at such temperature from 1 to 4 hours.At this stage in the method of the present invention, the nucleipreviously formed in the glass object develop into relatively largercrystals because of phase separation. The crystals formed provide theobject with sufiicient rigidity that the object does not sag even whenheld for long periods of time at a temperature considerably above thedeformation temperature of the object in its completely .Vitrified,glassy state. The amount of time that the object is held at its phaseseparation temperature will determine the amount of devitrification sothat such devitrification can be easily controlled. Thus, by controllingthe time that the object is maintained at its nucleation temperature andat its phase separation temperature, the amount of devitrification ofthe object can be controlled to achieve an object having the desiredproperties.

The heat treatment just described for converting a completely vitrifiedglass of the present invention to a partially devitrified glass is a twostep process which is illustrated as curve A in FIGURE 5. As previouslydescribed and as shown in FIGURE 5, the glass is heated from roomtemperature to the nucleation temperature of the glass, and ismaintained at the nucleation temperature .for a period of time. Theglass is then heated to its phase separation temperature, and held atthis temperature for a period of time sufficient to obtain the desireddevitrification. The glass is then cooled at a relatively slow rate.Instead of this two step heat treatment, a controlled devitrification ofthe glass of the present invention can be obtained by a one step processwhich is illustrated by curve B in FIGURE 5. This one step processcomprises heating the formed glass object at a relatively slow rate,such as at a rate of 200 to 360 F. per hour, from room temperature to atemperature between the nucleating temperature and the phase separationtemperature of the glass. The glass is maintained at this intermediatetemperature for a period substantially equal to the total time that theglass would be maintained at the nucleation temperature and the phaseseparation temperature in the two step process, so as to permitnucleation and phase separation at one time. The partially devitrifiedglass is then cooled at a relatively slow rate.

In the one and two step heat treatment schedules heretofore described,the heat treatment was started with the glass object being at roomtemperature. However, as illustrated by curve C in FIGURE 5, the heattreatment of the glasses of the present invention can be applied to theglasses straight from the hot forming molds without prior annealing ofthe articles and cooling of the glass articles to room temperatur Asillustrated by curve C, the glass object can be subjected to the twostep heat treatment schedule similar to that illustrated by curve A, butwith the glass object being heated to is nucleation temperature directlyfrom the hot forming mold. This heat treatment schedule is the mosteconomical of the three heat treatment schedules illustrated in FIGURE 5since it eliminates the need for annealing the glass object, and reducesthe time required to heat the glass object to its nucleationtemperature.

More specifically, a partially devitrified glass of the presentinvention may be obtained from a base composition of silica and potashusing titanium oxide as the nucleating agent. Referring to FIGURE 1,there is shown a triaxial diagram illustrating the percent by weight ofoxides in a batch which yields upon the proper heat treatment such apartially devitrified glass or" the present invention. As shown therein,the compounds may be present in the batch in the following ranges inpercent by weight of the total batch: Silica (SiO 5 to 95%, potash (K Oto 60% and titanium oxide (TiO 5 to 55%.

It is preferrtd to form the partially devitrified glass of the presentinvention from a composition containing a minimum of approximately 35%by weight of titanium oxide. Thus, a more preferred range of thecompounds is as follows: Silica 5 to 59%, potash 6 to 53% and titaniumoxide 35 to 55%. The preferred range of the compounds is the majorportion of the shaded area in the triaxial diagram of FIGURE 1 which ison the right hand side of the line A. This range of the compounds ispreferred since the compositions of the glass in the shaded A areasprojecting to the left hand side of line A in FIG- URE 1 are difficultto form.

Although the glasses described herein are specified in terms of thepercent of oxides of the various cations in the batch from which theglass is formed, and although the oxide forms are generally used inglass making, the exact compound in which the ions are introduced is ofminor importance in most glasses. Thus, the cations may be introduced asnitrates, oxolates or other chemical compounds. Therefore, it is to beunderstood that whenever oxides are mentioned as constituents of a glassbatch, other compounds containing the same cations may also be used.

Referring to Table 1, Examples 1 through 5 are specific compositions ofthe silica-potash-titanium oxide glass of the present invention. Theglasses of Examples 1 through 5 can be made in the manner previouslydescribed using the two step heat treatment illustrated by curve A inFIGURE 5, and using the various temperatures shown in Table II. Forexample, the glass of Example 1, which contains silica, 15% potash and35% titanium dioxide, can be made by mixing t e ingredients together,placing them in a crucible and heating the ingredients to a meltingtemperature of 2700 F. When the ingredients are completely melted, themolten glass is poured into a steel mold which is at a temperature of300 C. The formed glass article is then annealed by heating the articleto a temperature of 1100 F., and soaking the article at such atemperature for a period of 1 hour. The glass article is then cooled ata rate of approximately 200 F. per hour. At this point, the glassarticle is a transparent, completely vitrified glass. To form thepartially devitrified glass of the present invention, the glass objectis then heated to a nucleation temperature of 1350 1- and held at thenucleation temperature for a period of one-half hour to permit theformation of the nuclei. The glass object is then heated to a phaseseparation temperature of 1450 -F., and held at such a phase separationtemperature for a period of one-quarter of an hour to permit partialdevitrification of the glass. The glass object is then cooled at a rateof F. per hour to room temperature. The glasses or" Examples 2 through 5can be similarly formed using the temperatures shown in Table II.

Table III shows some of the properties of the glass compositions of thepresent invention before and after the glass is subjected to the heattreatment to partially devitrify the glass in accordance with thepresent invention. As shown in Table III, the glass composition of thepresent invention of Example 1 has a deformation temperature prior tothe heat treatment, i.e. as a completely vitrified glass, of 1365 F.,whereas its deformation temperature after being subjected to the heattreatment and being partially devitrified is 1750 F. The dielectricconstant of the glass of Example 1 before the heat treatment is 10,whereas after the heat treatment the partially devitrified glass has adielectric constant of 10.7. As can be seen from Table III, the glassesof Examples 2 through 5 likewise have increased deformation temperaturesand dielectric constants after being partially devitrified by the heattreatment of the present invention. Thus, the partially devitrifiedglasses of the present invention have improved physical and electricalproperties over the same compositions which are in their completelyvitrified state.

Table l Table I1 Melting Temp, F 2,700 2,500 2, 400 2,500 2, 400 2, 5502, 000 2, 400 Annealing Temp, F (1 hr, soak). 1,100 1, 050 1,050 1, 0001,000 1,000 1,050 900 Nucleation '1em F 1,350 1,300 2,200 1,250 1,1001,225 1,325 1,150 Nucleation Soak Time (II 4 4 4 Phase Separation Temp,1, 450 1,450 1,250 1,450 1,200 1,350 1,450 1, 300 Soak Time (Hrs) M 2 22 2 2 2 1 Cooling Rate, F./hr 100 100 100 100 100 100 100 100 Table IIIto 70%. As when using titanium oxide or niobium oxide as the nucleatingagent, it is preferred that the par- Dcrormation Dielectric De sitytially devitrified glassof the present inventlon contain a Temp-icmstallt minimum of approx1mately 35% of tantalum oxide. 15 Thus, thepreferred range of composition, as indicated by Before After BeforeAfter Before After the shaded area to the right hand side of line C inFIG- URE 3, is as follows: Silica 10 to 65%, potash 0 to 55% 1,365 1,75010 and tantalum oxide 35 to 70%. 1, 200 1,600 10.6 h 1, 285 1,550 11.4Example 7 in Table I is a specific composltlon of t e 17240 1,500 m7 '1silica-potash-tantalum oxide glass of the present inven- 1,240 1,50011.5 13 2. s3 2. l

tion. As indlcated 1n Table II, a partlally devltrlfied FIGURE 2 is atriaxial diagram of a silica-potash glass of the present invention usingniobium oxide as the nucleating agent. As shown therein, the compoundsmay be present in this glass of the present invention in the followingranges as percent by weight of the total: Silica (SiO to 95%, potash (K0) 0 to 60% and niobium oxide (Nb O 5 to 75%. As when using titaniumoxide as the nucleating agent, it is preferred to form the partiallydevitrified glass of the present invention from a composition containinga minimum of approximately 35% by weight of niobium oxide. Thus, a morepreferred range of the compounds, as indicated by the shaded area to theright hand side of the line B in FIG- URE 2, is as follows: Silica 10 to64%, potash 2 to 55% and niobium oxide 35 to 75%.

Referring to Table I, Example 6 is a specific composition of asilica-potash-niobium oxide glass of the present invention. Such apartially devitrified glass of the present invention is made insubstantially the same manner as previously described using the varioustemperature conditions set forth in Table II. Thus, the glass of Example6, which consists of 15% silica, 15% potash and 70% niobium oxide, canbe made by mixing the ingredients together, placing them in a crucibleand heating the ingredients to a melting temperature of 2550 F. When theingredients are completely melted, the molten glass is molded in aheated steel mold to form a glass article of the desired shape. Themolded glass article is then annealed by heating the article to anannealing temperature of 1000 F. and maintaining the article at such anannealing temperature for approximately 1 hour. The article is thencooled at a rate of approximately 200 F. per hour. The glass so formedis a transparent, completcly vitrified glass. To form the partiallydevitrified glass of the present invention, the glass article is heatedto a nucleation temperature of 1225 F., and held at such nucleationtemperature for a period of approximately /2 hour. The glass article isthen further heated to a phase separation temperature of 1350 F andmaintained at such a phase separation temperature for approximately 2hours to permit partial devitrification of the glass article. Thepartially devitrified glass article is then cooled at a rate ofapproximately 100 F. per hour to complete the formation of the partiallydevitrified glass of the present invention.

In addition to titanium oxide and niobium oxide, I have found thattantalum oxide can also be used as a nucleating agent. FIGURE 3 is atriaxial diagram of a silicapotash base glass using tantalum oxide asthe nucleating agent. As shown in FIGURE 3, such a glass has a range ofcomposition of its components based on percent by weight of the oxidesas follows: Silica (SiO 10 to 95 potash (K 0) 0 to 60% and tantalumoxide (Ta O 5 glass of the present invention can be made from thecomposition of Example 7, which is 20% silica, 20% potash and 60%tantalum oxide, by mixing the ingredients together, placing them in acrucible and heating the ingredients to a melting temperature of 2600 F.After the ingredients are completely melted, the molten glass is castinto a desired shape in a heated steel mold. The formed glass object isthen annealed by heating the object to an annealing temperature of 1050F., and maintaining the object at such an annealing temperature forapproximately one hour. The glass object is then cooled at a rate ofapproximately 200 F. per hour until the object reaches room temperature.To partially devitrify the glass object, the object is subjected to theheat treatment of heating the object to a nucleation temperature or"approximately 1325 F., and maintaining the glass object at such atemperature for approximately of an hour. The glass object is thenheated to a phase separation temperature of 1450 F. and maintained atsuch phase separation temperature for approximately two hours. Theobject is then cooled at a rate of approximately 100 F. per hour untilthe partially tie-vitrified glass object of the present inventionreaches room temperature.

Another base glass which can be formed as a partially devitrified glassusing the nucleating agents of the present invention when subjected tothe heat treatment of the present invention, is shown in FIGURE 4. Sucha base glass is a germanium oxide-potash glass, and as shown in FIGURE 4uses tantalum oxide as the nucleating agent. The range of composition ofthe components of such a glass which can be formed as a partiallydevitrified glass of the present invention is as follows: Germaniumoxide (GeO 10 to potash (K 0) O to 50% and tantalum oxide (T21 O 10 to60%. A preferred range of composition which uses a minimum ofapproximately 35% of the tantalum oxide nucleating agent is illustratedby the shaded area to the right hand side of line D in FIGURE 4, and isas follows: Germanium oxide 10 to 65%, potash 0 to 50% and tantalumoxide 35 to 60%.

Example 8 in Table I is a specific composition of the germaniumoxide-potash-tantalurn oxide glass of the present invention which can beformed as a partially devitrified glass. As indicated in Table II, theglass of Example 8, which is 25% germanium oxide, 25% potash and 50%tantalum oxide, can be formed as a partially devitrified glass by mixingthe ingredients together, placing them in a crucible and heating theingredients to a melting temperature of 2400 F. When the ingredients arecompletely melted, the molten glass is cast into a desired shape in aheated steel mold. The formed glass object can then be annealed byheating the object to an annealing temperature of 900 F. and maintainingthe object at such a temperature for a period of approximately one hour.The glass object is then cooled at a rate of approximately 200 F. perhour until the object reaches room temperature. The annealed glassobject is then subjected to the heat treatment of the present inventionby heating the glass object to a nucleation temperature of 1150 F., andmaintaining the glass object at such a temperature for approximatelythree-quarters of an hour. The temperature of the glass object is thenincreased to the phase separation temperature of 1300 F., and the glassobject is maintained at the phase separation temperature forapproximately one hour to permit partial devitrification. The partiallydevitrified glass object is then cooled at a rate of approximately 100F. per hour until the glass reaches room temperature.

Although Table III shows the improvement in tie specific properties ofthe glasses of Examples 1 to 5, it should be understood that thepartially devitriiied glasses of Examples 6, 7 and 8 have similarimprovements in their properties. Thus, each of the partiallydevitrified glasses of the present invention has a higher deformationtemperature and a higher dielectric constant than the same glass in itscompletely vitrified form.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof and,accordingly, reference should be made to the appended claims, ratherthan to the foregoing specification as indicating the scope of theinvention.

I claim:

by Weight 5 to 65% silica, to 55% potash and a nucleating agent selectedfrom the group consisting of 35 to 55% titanium oxide, 35 to 75% niobiumoxide and 35 to 70% tantalum oxide.

2. A partially devitrified glass consisting essentially of by Weight to59% silica (SiO 6 to 53% potash (K 0) and 35 to 55% titanium oxide (TiO3. A partially devitrified glass consisting essentially of by Weight to64% silica (SiO 2 to 55% potash (K 0) and to 75% niobium oxide (Nb O 4.A partially devitrified glass consisting essentially of by Weight 10 to65% silica (SiO 0 to potash (K 0) and 35 to 70% tantalum oxide (Ta O 1.A partially devitrified glass consisting essentially of 5. A partiallydcvitrified glass consisting essentially of by Weight 10 to 90%germanium oxide (GeO 0 to 50% potash (K 0) and 10 to tantalum oxide 2 5)6. A partially devitrified glass consisting essentially of by weight 10to germanium oxide (GeO 0 to 50% potash (K 0) and 35 to 60% tantalumoxide 2 5)- References Cited in the file of this patent UNITED STATESPATENTS 1,607,817 Dennis Nov. 23, 1926 2,425,403 Sun Aug. 12, 19472,920,971 Stookey Jan. 12, 1960

1. A PARTIALLY DEVITRIFIED GLASS CONSISTING ESSENTIALLY OF BY WEIGHT 5TO 65% SILICA, 0 TO 55% POTASH AND A NUCLEATING AGENT SELECTED FROM THEGROUP CONSISTING OF 35 TO 55% TITANIUM OXIDE, 35 TO 75% NIOBIUM OXIDEAND 35 TO 70% TANTALUM OXIDE.